Among the points corresponding to number 1,2,...,2n on the real line, n are colored in blue and n in red. Let a1,a2,...,an be the blue points and b1,b2,...,bn be the red points. Prove that the sum ∣a1−b1∣+...+∣an−bn∣ does not depend on coloring , and compute its value. :roll: combinatorics unsolvedcombinatorics